FIG. 7 illustrates an outline of a three-phase AC motor drive control device described in Patent Document 1.
This drive control device is mounted on a hybrid automobile or the like, for example. This drive control device controls driving of an inverter by switching a control mode among three control modes, that is, a PWM (pulse width modulation) current control mode and a PWM voltage phase control mode for driving the three-phase AC motor with high efficiency and a rectangular wave voltage phase control mode for improving a three-phase AC motor output.
The PWM current control mode is a control mode when switches 26 and 28 are both switched to the upper side in FIG. 7. In this PWM current control mode, voltage amplitude |V| and a voltage phase Ψ are set such that the current value supplied to the three-phase AC motor 38 and the command current value match each other. An alternating pulse voltage is generated in accordance with the voltage amplitude |V| and the voltage phase Ψ, and the alternating pulse voltage is applied to the three-phase AC motor 38.
In the PWM voltage phase control mode, the voltage phase Ψ is set in accordance with temporal changes of the voltage amplitude |V|. An alternating pulse voltage is generated in accordance with the set voltage phase Ψ, and the alternating pulse voltage is applied to the three-phase AC motor 38 by switching the switch 26 to the lower side and the switch 28 to the upper side in FIG. 7.
In the rectangular wave voltage phase control mode, the voltage amplitude |V| is determined by a DC battery voltage Vdc, and the voltage phase Ψ is set in accordance with a command torque value. A rectangular wave voltage is generated on the basis of the set voltage amplitude |V| and voltage phase Ψ, and the rectangular wave voltage is applied to the three-phase AC motor 38 by switching the switch 28 to the lower side in FIG. 7.
Moreover, in the drive control device, a command torque value generated in accordance with an accelerator pedal manipulation amount and a brake pedal depression amount in a vehicle control device (not shown) is input into a current command generating section 12 and an adder 13. The current command generating section 12 generates command current values Iq and Id on the basis of the input command torque value and outputs the generated command current values Iq and Id to a current controller 14. The current controller 14 executes proportional-integral control on the basis of the input command current values Iq and Id and a current value detected by a current sensor 40 to generate the voltage amplitude |V| and the voltage phase Ψ, which will be used as voltage command values. The switch 26 selectively switches whether or not to input the voltage amplitude |V| and the voltage phase Ψ generated by the current controller 14 into a PWM circuit 30. If the voltage amplitude |V| and the voltage phase Ψ are input, the PWM circuit 30 generates a sine wave on the basis of the voltage amplitude |V| and the voltage phase Ψ. Moreover, the PWM circuit 30 generates a switching command on the basis of comparison between the sine wave and a triangular wave set in advance and outputs the switching command to an inverter 36 through the switch 28. The inverter 36 generates an alternating pulse voltage in accordance with the switching command output from the PWM circuit 30 and applies the alternating pulse voltage to the three-phase AC motor 38 as a driving voltage.
The current sensor 40 detects a current flowing through the three-phase AC motor 38 by application of the driving voltage and outputs the detected current value to an adder 24. The adder 24 receives the current value detected by the current sensor 40 and the command current value generated by the current command generating section 12. The adder 24 generates a difference between the input command current value and the detected current value, that is, a current deviation ΔI and outputs the current deviation ΔI to a current matching determining section 22. The current matching determining section 22 switches the switch 26 if the detected current value matches the command current value.
On the other hand, a torque value detected by torque detecting means 20 each time together with the command torque value is input into the adder 13. The adder 13 generates a difference between the torque values, that is, a torque deviation ΔT and supplies the generated torque deviation ΔT to a voltage phase controller 18. The voltage phase controller 18 generates the voltage phase Ψ in accordance with the torque deviation ΔT. The voltage phase controller 18 generates a rectangular wave voltage phase Ψ in the rectangular wave voltage phase control mode and generates the voltage phase Ψ of an alternating pulse voltage in the PWM voltage phase control mode.
Moreover, a voltage amplitude controller 16 supplies the voltage amplitude |V| also to a voltage amplitude determining section 34. The voltage amplitude determining section 34 compares the supplied voltage amplitude |V| with voltage amplitude corresponding to the rectangular wave voltage and switches the switch 28 on the basis of the comparison result.
A rectangular wave generating section 32 generates a rectangular wave voltage, which will be used as a switching command to the inverter 36, on the basis of the voltage phase Ψ input from the voltage phase controller 18. When such a switching command is transmitted to the inverter 36 through the switch 28, the inverter 36 applies a switched alternating (AC) voltage to the three-phase AC motor 38 on the basis of the rectangular wave voltage. As a result, the three-phase AC motor 38 is driven.
As described above, the drive control device appropriately controls driving of the three-phase AC motor 38 in accordance with the traveling environment of the automobile by selectively switching the control mode among the PWM current control mode, the PWM voltage phase control mode, and the rectangular voltage phase control mode.
The rectangular wave voltage phase control mode is usually used in a high rotation range of the three-phase AC motor 38. Therefore, its control calculation needs to be completed in short time in order to ensure control responsiveness in the rectangular wave voltage phase control mode. Conventionally, the calculation has been performed through the following processing.
That is, in the rectangular wave voltage phase control mode, the rectangular wave voltage (switched alternating (AC) voltage), which is an output in the U-phase, the V-phase, and the W-phase, of the inverter 36 is successively switched by a 180° cycle in each phase in a mode synchronized with a rotor position (rotor angle) of the three-phase AC motor 38, as illustrated in FIG. 8.
In such switching control, first, a current flowing through the three-phase AC motor 38 is detected at an intermediate point of time t3 between a point of time t1 when an output in the V-phase is off and a point of time t2 when an output in the U-phase is on, that is, when the rotor position of the three-phase AC motor 38 reaches an angle θ1. Subsequently, the voltage phase Ψ according to the torque deviation ΔT at that time is calculated through a torque feedback calculation on the basis of the detected current. An output switching angle in each next phase is determined on the basis of the voltage phase Ψ calculated as above, and next interruption setting is performed by the determined output switching angle so that the drive control of the three-phase AC motor 38 is executed. As described above, the switching command for generating the three-phase output is calculated during the period in which the rotor angular position changes from an interruption angle θ1 to an interruption end angle θ2 (approximately 30°) as illustrated as a period t3-t2 in FIG. 8.
Such calculation of the switching command usually takes time of 70 μsec. However, if the three-phase output is switched in the mode synchronized with the rotor position as described above, time corresponding to the time between each interruption angle, that is, time allowed for calculation of the switching command for the next one cycle becomes shorter as the rotation speed of the three-phase AC motor 38 is raised. If the rotation number of the four-pole-pair three-phase AC motor is 20,000 rpm, for example, time corresponding to the time between the interruption angles (t3-t2) becomes 60 μsec or less, which is shorter than the time usually required for the calculation of the switching command. As a result, the calculation is not completed in the time (t3-t2), the next rectangular wave cannot be generated, and a switching element does not operate for one cycle. Thus, if the calculation of the switching command is not completed in each time corresponding to the time between the interruption angles in the rectangular wave voltage phase control, the rectangular wave voltage is lost, which might incur loss of synchronism of the three-phase AC motor, for example, and the drive control device can no longer execute appropriate inverter control.